The instant invention relates to gyroscopes and, more particularly, to controlling heat convections of a fluid that supports a sealed inner container which houses a navigational gyroscope.
Precision gyros used in inertial navigation equipment are designed with a low friction output axis bearing so that gyro precision is not falsely indicated by gyro case rotation. A commonly used aid in making a low friction output axis bearing is the relief of bearing loads by enclosing the gyro wheel and motor in a sealed container and surrounding this container with a liquid. The output axis bearing may be jewel and pivot, a magnetic bearing, or of some other type. The design of the gyro wheel container is such that it is of the same density as the liquid in which it is immersed. This wheel container is therefore called a "float." To the degree that the float density matches the fluid density, gravity and acceleration forces on the float are cancelled by buoyancy forces. Thus, bearing loads are made very small.
Although floatation is a great benefit to the output axis bearing, the fluid is a source of error torque on the float. A temperature gradient has been recognized as a source of convection in the fluid and of viscous torque on the gyro. In order to keep such torque constant, temperature control of the gyro is used. It is found that temperature sensitivity (that is, gyro drift change per degree change in temperature or temperature gradient) is large compared to desired accuracy so that very precise temperature control is required. Gyro temperature sensitivity has been analyzed by assuming that the fluid gap is sufficiently small that a mean temperature may be used and that the significant feature is the difference in the mean fluid temperature across the gyro.
Detailed examination of heat convection currents (hereinafter referred to as "convections" or "heat convections") show that convection fluid velocity is proportional to the temperature difference across the fluid gap between the float and the case. Convection can be supressed by controlling temperature such that the temperature of the gyro case adjacent to the fluid is held at the same temperature as the gyro float. Gyro temperature control in this manner will reduce gyro temperature sensitivity to a small fraction of present values by largely eliminating convection and resulting torque variations with temperature variation.
Specifically, a floated gyro has a very narrow fluid gap, with 0.005 to 0.010 of an inch being typical. The fluid is dense and viscous. Temperature difference across the fluid gap is typically from approximately 5 degrees to approximately 10 degrees. Temperature assymetries arise from changes in ambient air temperature. The above-mentioned torque variation can be reduced to a very small and insignificant value by controlling temperature, so that the temperature difference across the fluid gap is zero or near zero.
Therefore, what is needed in the art and is not presently available is some way to maintain the temperature difference across the fluid gap to zero or near zero.